Brown Rust Spots on Bush Bean Plant

(Question)

Hi there,

I have a three bush bean plants growing in a container. They were initially in their own individual smaller containers but I moved them to larger pot after a while. They were extremely root bound by the time I transplanted them but still managed to grow and produce some beans. The plants are still producing but some of the leaves have started to turn yellow while others have brown spots and are drying up.

I’ve attached a picture of two of the leaves. The pot has drainage holes but I rarely have to water because the potting mix stays moist below the surface. I use a moisture meter to check deep within the pot. I know these plants will be done producing soon so I’m not worried, but I’m curious to know what the issue might be so I can avoid making the same mistake next time. I have cucumber plants nearby that are about 6-7 inches tall that also are showing leaf spotting, transparent areas on the leaves and drying out, so I’m thinking I might be doing something wrong. The plants are in front of a west facing window and I intended to move them outside when safe to do so.

Thanks!

(Answer)

Thank you for your question

From the picture you sent it looks like your plants have Pseudomonas syringae pv. Phaseolicola or halo blight.  The lesions of a halo blight infected plants have a large pale yellow halo around them. This halo may be 1/2 inch in diameter. When lesions mature, the dead tissue in the center falls out resulting in a shot-hole or tattered leaf appearance. The bacterial fluid found in these lesions is cream or silver colored. Infected pods may be twisted or kinked at the infection point. The development of the lesions is associated with temperatures between 15 – 20 degrees C.

These bacteria are introduced by infected seed. Damp conditions favour its development.

Some of the things you might consider to help confirm whether this is actually halo blight are:

  • The time you planted the vegetables because different types of blight affect the plants at different times of the growing cycle.
  • The temperature of the room the pots are growing in
  • Whether the spots on the cucumbers look exactly like the ones on the beans because cucumbers are not affected by halo blight.

If you decide that your bush plants do have halo blight these are some of the things you can do to prevent this problem in the future:

  • Destroy the affected plants at the end of the season.
  • Sterilize the pots with a weak solution of bleach.
  • Purchase certified seed; plant resistant varieties
  • Avoid watering over the plants – water the soil directly instead

Below are some sites that have further information about plant diseases affecting bush beans:

Bean- Diseases and Pests

https://www.apsnet.org/publications/imageresources/Pages/fi00227.aspx

http://learningstore.uwex.edu/assets/pdfs/A3374.PDF